JP5921119B2 - X-ray diagnostic equipment - Google Patents

Description

  Embodiments described herein relate generally to an X-ray diagnostic apparatus and an X-ray diagnostic stent.

  As one of imaging by an X-ray diagnostic apparatus, imaging using a stent is known. The stent is formed into a mesh-like cylinder using struts having a wire-like structure. A typical stent used with an X-ray diagnostic apparatus includes an intracranial stent.

  The intracranial stent struts are very thin and it is difficult to observe the stent itself with an X-ray diagnostic apparatus. Specifically, the cross-sectional diameter of the strut of the intracranial stent is about 60 μm. Therefore, the conventional stent is provided with a marker so that an approximate position can be grasped by imaging with an X-ray diagnostic apparatus. Specifically, four markers are provided at equal intervals on the same circle forming one end of the stent, and another four markers are provided at a position on the other end side when the four markers are projected in the longitudinal direction of the stent. .

  On the other hand, the X-ray diagnostic apparatus includes an X-ray detector having higher spatial resolution than an X-ray CT (computed tomography) apparatus. However, the fluoroscopic image and the captured image using the X-ray diagnostic apparatus can hardly be observed except for the marker. However, when three-dimensional (3D) imaging is performed, it is possible to observe the struts of the stent.

JP 2011-104353 A

  However, in the conventional X-ray diagnostic apparatus, it may be difficult to suppress the positioning error of the rotating system equipped with the X-ray detector and the X-ray tube to 100 to 150 μm. That is, the position of the X-ray projection system slightly changes with each rotation due to factors such as vibration caused by rotation of the rotating system and slight defocus due to changes in the amount of heat of the tube of the X-ray tube. For this reason, the reproducibility of the rotating system within the range of 100 to 150 μm cannot be guaranteed.

  On the other hand, when using a method of correcting vibrations using a vibration table collected in the past, which is generally used for correcting vibrations in 3D imaging by an X-ray diagnostic apparatus, it has a fine structure. In order to depict the struts of a stent, the reproducibility of a rotating system of 100 to 150 μm is required. In particular, in order to clearly depict the struts, it is considered that the rotational reproducibility of 50 μm or less corresponding to 1/4 or less of 1 pixel is necessary for the support device of the rotating system.

  Therefore, attempts have been made to improve the stability of the X-ray diagnostic apparatus mechanically, and to detect a minute change in the position of the rotating system and to correct the detected change in position. However, these attempts have a problem that the cost of the X-ray diagnostic apparatus is increased.

  In addition, there is a problem that it is difficult to depict a strut of a stent having a fine structure when a subject to be a patient moves even during imaging. In this case, even if the stability of the X-ray diagnostic apparatus is improved or the change in the position of the rotating system is corrected, it is difficult to clearly depict the struts of the stent.

  An object of the present invention is to provide an X-ray diagnostic apparatus and an X-ray diagnostic stent that can depict a fine stent strut by a simpler technique in imaging using a stent.

An X-ray diagnostic apparatus according to an embodiment of the present invention includes a data collection unit and a data processing unit. The data collection means collects X-ray projection data corresponding to the plurality of directions from the subject by exposing the subject into which a stent provided with a plurality of markers is inserted from a plurality of directions. Data processing means obtains the spatial position of at least one marker of the plurality of markers on the basis of the first three-dimensional image data generated by the first image reconstruction processing with respect to the X-ray projection data, said plurality for each X-ray projection data corresponding to the direction of the projection plane of the marker corresponding determined based and the projection position of the spatial position of the marker to the projection plane of the X-ray projection data on the X-ray projection data A shift amount with respect to the above two-dimensional position is obtained, and second three-dimensional image data is generated by a second image reconstruction process for the X-ray projection data accompanied by correction using the shift amount .

1 is a configuration diagram of an X-ray diagnostic apparatus according to a first embodiment of the present invention. The perspective view which shows the structure of the conventional stent which can be used with the X-ray diagnostic apparatus shown in FIG. The perspective view which shows the structural example of the stent for X-ray diagnosis which concerns on embodiment of this invention which can be used with the X-ray diagnostic apparatus shown in FIG. The perspective view which shows another structural example of the stent for X-ray diagnosis which concerns on embodiment of this invention which can be used with the X-ray diagnostic apparatus shown in FIG. The flowchart which shows the flow at the time of imaging of the subject which inserted the stent by the X-ray diagnostic apparatus shown in FIG. The figure which shows the definition of the coordinate system and parameter used in the data processing in the data processing system shown in FIG. The block diagram of the X-ray diagnostic apparatus which concerns on the 2nd Embodiment of this invention.

  An X-ray diagnostic apparatus and an X-ray diagnostic stent according to an embodiment of the present invention will be described with reference to the accompanying drawings.

(First embodiment)
FIG. 1 is a configuration diagram of an X-ray diagnostic apparatus according to the first embodiment of the present invention.

  The X-ray diagnostic apparatus 1 includes an imaging system 2, a control system 3, a data processing system 4, and a console 5. The imaging system 2 includes an X-ray tube 6, an X-ray detector 7, a C-type arm 8, a base 9 and a bed 10. The data processing system 4 includes an A / D (analog to digital) converter 11, a computer 12, a D / A (digital to analog) converter 13, and a display device 14.

  The X-ray tube 6 and the X-ray detector 7 are fixed to both ends of the C-arm 8 so as to face each other across the bed 10. The C-type arm 8 is held by a base 9. The base 9 includes a motor 9A and a rotation mechanism 9B. By driving the motor 9A and the rotation mechanism 9B, the X-ray tube 6 and the X-ray detector 7 are rotated at high speed like a propeller to a desired position together with the C-type arm 8. Can be made.

  As the X-ray detector 7, a flat panel detector (FPD) or an image intensifier TV (I.I.-TV: image intensifier TV) can be used. The output side of the X-ray detector 7 is connected to the A / D converter 11 of the data processing system 4.

  The control system 3 is a device that drives and controls the photographing system 2 by outputting a control signal to each component constituting the photographing system 2. The control system 3 is connected to a console 5 as an input device, and instruction information such as imaging conditions to the control system 3 can be input from the console 5.

  The imaging system 2 sequentially emits X-rays at different angles from the rotatable X-ray tube 6 to the subject O set on the bed 10 under the control of the control system 3 from a plurality of directions. X-rays that have passed through the subject O are sequentially collected by the X-ray detector 7 as X-ray projection data.

  In particular, the X-ray diagnostic apparatus 1 is configured to perform imaging of an imaging region including a stent inserted into an imaging region of the subject O and draw a strut constituting the stent. That is, the imaging system 2 can collect X-ray projection data from a region including a stent inserted in the imaging region of the subject O.

  FIG. 2 is a perspective view showing the structure of a conventional stent that can be used with the X-ray diagnostic apparatus 1 shown in FIG.

  As shown in FIG. 2, the conventional stent 15 is configured by symmetrically and equally arranging four markers 17 on both ends of a strut 16 formed in a mesh tube shape. The stent 15 having such a configuration is inserted into a blood vessel including an aneurysm, such as an intracranial region, and is mainly used for performing treatment in the blood vessel more safely.

  The marker 17 is made of a material that exhibits a CT value higher than that of a reference material existing around the imaging region. For example, in the case of a stent used in the cranium, it is practical to configure the marker 17 with a material having a CT value higher than that of bone or teeth.

  For this reason, when X-ray projection data is collected from the region including the stent 15, it is possible to generate image data in which the region corresponding to the marker 17 is depicted as a low signal value. In this case, the imaging system 2 emits X-rays from the subject O in a plurality of directions by exposing the subject O into which the stent 15 provided with the plurality of markers 17 is inserted from a plurality of directions. It functions as a data collection means for collecting data. However, if the X-ray diagnostic apparatus 1 is provided with a similar function as data collection means, the data collection means may be constituted by other components.

  In the conventional stent 15 shown in FIG. 2, four markers 17 are arranged at equal intervals on the same circle at each end. Therefore, depending on the projection direction, a plurality of markers 17 may overlap. For example, if X-ray projection data is collected from the direction P1 perpendicular to the axial direction L, which is the longitudinal direction of the strut 16, all the markers 17 may overlap. In such a case, even if the image data is reconstructed from the X-ray projection data, it may be difficult to distinguish the markers 17 from each other on the image data.

  Therefore, it is preferable to arrange the plurality of markers 17 at at least one end of the strut 16 so that at least one of the markers 17 does not overlap when projected in a single direction.

  FIG. 3 is a perspective view showing a structural example of an X-ray diagnostic stent according to an embodiment of the present invention that can be used with the X-ray diagnostic apparatus 1 shown in FIG.

  A stent 15A shown in FIG. 3 shows an example in which three markers 17 are arranged symmetrically and equally on both ends of a strut 16 formed in a mesh shape. As shown in FIG. 3, when the number of markers 17 is an odd number, a plurality of markers 17 are arranged so that at least one of them does not overlap when projected in at least a single direction P2 different from the axial direction L of the struts 16. can do.

  If the number of the markers 17 provided at one end of the strut 16 is 5 or more, there is a possibility that the structure of the stent and the manufacturing process become complicated. Suitably placed at one end. That is, if the three markers 17 are arranged at at least one end of the strut 16, it is possible to prevent all the markers 17 from overlapping when projected in a single direction P2 different from the axial direction L of the strut 16.

  Further, the plurality of markers 17 can be respectively disposed at both ends of the strut 16 so as not to overlap each other when the positions are projected in the axial direction L of the strut 16.

  FIG. 4 is a perspective view showing another structural example of a stent for X-ray diagnosis according to an embodiment of the present invention that can be used with the X-ray diagnostic apparatus 1 shown in FIG.

  A stent 15B shown in FIG. 4 shows an example in which four markers 17 are equally arranged on both ends of a strut 16 formed in a meshed cylindrical shape. However, when the four markers 17 once provided on the side are projected along the axis L of the strut 16, the four markers 17 provided on the other end side are rotated by a predetermined angle θ. For this reason, when the positions of all the markers 17 are parallel-projected in a single direction including the axial direction L of the strut 16, it is possible to prevent all the markers 17 from overlapping.

  In this way, if the arrangement of the four markers 17 provided on one of the struts 16 of the conventional stent 15 is shifted with respect to the other four markers 17, the markers 17 can be connected to each other without changing the number of markers 17. Overlap can be prevented.

  From the viewpoint of improving the effect of preventing the overlapping of the markers 17 and facilitating the manufacturing method, when projected in the axial direction L of the strut 16, the struts 16 are positioned at both ends so that they are rotated by 45 degrees. It is preferable to arrange four markers 17 for each.

  Of course, when the three markers 17 are provided at both ends of the strut 16 and the position of the marker 17 on one end side is projected in the axial direction L of the strut 16, it does not overlap with the position of the marker 17 on the other end side. Good. Even in this case, from the viewpoint of improving the effect of preventing the overlapping of the markers 17 and facilitating the manufacturing method, the struts 16 are positioned so as to be rotated by 60 degrees when projected in the axial direction L of the struts 16. It is preferable to arrange three markers 17 at both ends. In addition, it is also possible to provide different numbers of markers 17 at both ends of the strut 16.

  Next, detailed functions of the data processing system 4 will be described.

  The output side of the A / D converter 11 of the data processing system 4 is connected to the input side of the computer 12. On the other hand, a display device 14 is connected to the output side of the computer 12 via a D / A converter 13. The computer 12 is connected to the console 5. Then, instruction information necessary for data processing can be input to the computer 12 by operating the console 5.

  Furthermore, the computer 12 reads the program to thereby filter the filtering unit 18, the first image reconstruction unit 19, the 3D marker identification unit 20, the marker projection unit 21, the 2D marker identification unit 22, and the second image reconstruction unit 23. , Functions as a 3D image processing unit 24, an affine transformation unit 25, and a LUT (Look Up Table) 26. However, in order to obtain these functions, the data processing system 4 may be configured using a circuit.

  The filtering unit 18 performs high-frequency emphasis filtering or the like on the X-ray projection data input to the computer 12 from the X-ray detector 7 via the A / D converter 11 or data generated based on the X-ray projection data. It has a function of performing necessary filter processing.

  The first image reconstruction unit 19 performs an image reconstruction process based on a plurality of X-ray projection data corresponding to a plurality of directions input to the computer 12 from the X-ray detector 7 via the A / D converter 11. By executing this function, volume data is reconstructed as first 3D image data from X-ray projection data corresponding to a plurality of directions.

  The 3D marker identification unit 20 is based on the first 3D image data generated by the first image reconstruction unit 19 and is at least one marker among the plurality of markers 17 provided on the stents 15, 15 </ b> A, 15 </ b> B. It has a function of identifying 3D positions in 17 3D coordinate systems. The spatial positions of the single or plural markers 17 can be obtained by threshold processing for the first 3D image data. That is, the CT value of the marker 17 is higher than the reference substance. For this reason, if the point or area where the pixel value corresponding to the CT value of the first 3D image data is larger than the threshold value is specified by threshold processing, the spatial position of the marker 17 on the first 3D image data is identified. be able to.

  However, if a substance other than the marker 17 having a CT value higher than that of the reference substance is present in the imaging region, the position of the marker 17 may be erroneously recognized by threshold processing for identifying the position of the marker 17. For example, in the case where a metal exists as a dental treatment trace, if a portion higher than the CT value of a tooth is extracted by threshold processing, the metal portion may be erroneously recognized as the marker 17.

  Therefore, the 3D marker identification unit 20 uses the threshold process for the first 3D image data to temporarily identify the marker 17 candidate and exclude an error that excludes a point or region other than the marker 17 erroneously recognized as the marker 17 candidate. A function for executing processing can be provided. The error processing for removing the candidate of the marker 17 erroneously recognized based on the first 3D image data is executed based on the geometric information of the plurality of markers 17 provided on the stents 15, 15A, 15B. be able to.

  Specifically, the size and shape of each marker 17 provided on the stent 15, 15A, 15B, the distance between other markers 17, the distance from the center of the strut 16, and the center of the first 3D image data Since the geometric information such as the distance from is already known, the marker 17 candidate at a position that cannot be the position of the marker 17 based on the known information can be excluded as a misrecognized candidate. Thereby, the metal area | region etc. which exist as a dental treatment trace can be excluded from the marker 17 candidate.

  The marker projection unit 21 obtains a 2D projection position when the 3D spatial position of the marker 17 on the first 3D image data obtained by the 3D marker identification unit 20 is projected on the projection plane of each X-ray projection data. It has a function. In other words, the marker projection unit 21 has a function of calculating the projection position of the X-ray projection data of the 3D space position of the marker 17 on each projection plane. The calculation of the 2D projection position of the marker 17 on each projection plane can be performed based on the spatial coordinate information of the projection system used for collecting each X-ray projection data.

  However, as described above, depending on the projection direction of the X-ray projection data, the 2D projection positions of the markers 17 that are different from each other may overlap or may be difficult to distinguish. In particular, when the conventional stent 15 as shown in FIG. 2 is used, it is often difficult to distinguish the 2D projection positions of different markers 17.

  Therefore, the marker projection unit 21 calculates the distance between the 2D projection positions of the markers 17 that are close to each other on the projection plane, and performs error processing to exclude the calculated distance from the calculation target of the 2D projection position when the calculated distance is equal to or less than the threshold value. Can be done.

  The 2D marker identification unit 22 uses each of the markers 17 provided on the stents 15, 15 </ b> A, and 15 </ b> B based on a plurality of X-ray projection data corresponding to a plurality of directions input from the X-ray detector 7 to the computer 12. The correction amount is a shift amount between the function for identifying the 2D position on the projection plane, the 2D projection position of the X-ray projection data of the spatial position of the marker 17 on the projection plane, and the 2D position of the identified marker 17. It has the required function.

  It is sufficient that the marker 17 to be identified as the 2D position is the marker 17 corresponding to the 2D projection position calculated by the marker projection unit 21 and not excluded by the error processing. Therefore, the actual 2D position of the marker 17 may be identified from the X-ray projection data within the range near the 2D projection position calculated by the marker projection unit 21. Therefore, the 2D marker identification unit 22 is configured to acquire the 2D projection position of the marker 17 from the marker projection unit 21.

  The actual 2D position of the marker 17 on the X-ray projection data appears as a slight local minimum of the signal. Therefore, the 2D position of the marker 17 can be identified by arbitrary signal processing for detecting a small minimum value and a position corresponding to the minimum value with high accuracy.

  Further, instead of calculating the distance between the 2D projection positions of the adjacent markers 17 in the marker projection unit 21, the distance between the actual 2D positions of the adjacent markers 17 identified in the 2D marker identification unit 22 is calculated. May be. In this case, the 2D marker identification unit 22 calculates the distance between the 2D positions of the markers 17 that are close to each other on the projection plane, and when the calculated distance is equal to or less than the threshold, the shift amount of the 2D position with respect to the 2D projection position, that is, An error process for excluding the correction data from the calculation target is performed.

  The second image reconstruction unit 23 performs a second image reconstruction process on the X-ray projection data by performing a second image reconstruction process with correction using the correction data obtained by the 2D marker identification unit 22. It has a function of generating image data.

  That is, the positional deviation amount of the 2D projection position of the marker 17 from the actual 2D position can be considered as an error in the reproducibility of the position of the marker 17. Therefore, by performing correction processing for canceling the positional deviation amount of the marker 17 on the X-ray projection data corresponding to each projection direction, imaging based on the positioning accuracy error in the imaging system 2 and the movement of the subject O is performed. A minute positional shift of the part can be corrected. Then, the second 3D image data with higher spatial resolution can be generated by the second image reconstruction process based on the X-ray projection data after correcting the fine positional deviation.

  In addition, in the marker projection part 21 or the 2D marker identification part 22, when the error process which excludes the 2D projection position or 2D position of the marker 17 with a possibility of overlapping is performed, the correction data corresponding to some markers 17 The position correction process is executed using. That is, among the plurality of markers 17, the distance between the 2D projection positions of the markers 17 that are close to each other on the 2D projection plane or the actual 2D position or the distance between the actual 2D positions is larger than the threshold. The second image reconstruction process with correction is executed using only the shift amount between the 2D projection position to be performed and the actual 2D position.

  Thus, by providing the marker projection unit 21 or the 2D marker identification unit 22 with a function of executing error processing, even if some of the markers 17 overlap, highly accurate position correction processing based on the position information of the markers 17 is performed. Can be executed. In particular, if the stents 15A and 15B shown in FIGS. 3 and 4 are used, even if some of the markers 17 overlap each other on the projection plane, highly accurate and appropriate correction processing is performed based on the position information of the other markers 17. It can be carried out.

  The 3D image processing unit 24 is based on one or both of the first 3D image data generated by the first image reconstruction unit 19 and the second 3D image data generated by the second image reconstruction unit 23. It has a function of generating 2D image data for display by 3D image processing and a function of displaying the generated 2D image data for display on the display device 14 via the D / A converter 13.

  Examples of 3D image processing include maximum intensity projection (MIP) processing, multi-planar reconstruction (MPR) processing, volume rendering (VR) processing, and surface rendering (SR). Various processes for generating 2D image data from 3D image data, such as rendering) processing, can be mentioned. These types of image processing and image processing conditions can be set by inputting instruction information from the console 5 to the 3D image processing unit 24.

  The affine transformation unit 25 has a function of executing affine transformation processing such as rotation, movement, enlargement and reduction on the 2D image data generated by the 3D image processing unit 24 based on the instruction information input from the console 5. The image data after the affine transformation process is output to the display device 14 via the D / A converter 13. In other words, the affine transformation unit 25 has a function of rotating, moving, enlarging and reducing the 2D diagnostic image displayed on the display device 14 in accordance with the instruction information input from the console 5 as an input device.

  The LUT 26 stores gradation information for performing gradation conversion of image data, and has a function of performing gradation conversion of image data to be displayed on the display device 14 by referring to the gradation information. .

  In the above example, at least one marker 17 out of the plurality of markers 17 based on the first three-dimensional image data generated by the computer 12 having read the program by the first image reconstruction process on the X-ray projection data. And the shift amount between the projection position of the marker 17 on the projection plane of the X-ray projection data and the two-dimensional position of the corresponding marker 17 obtained based on the X-ray projection data is used. It functions as data processing means for generating second 3D image data by second image reconstruction processing for X-ray projection data with correction. However, if the X-ray diagnostic apparatus 1 is provided with a similar function as a data processing unit, the data processing unit may be configured with other components.

  Next, the operation and action of the X-ray diagnostic apparatus 1 will be described.

  FIG. 5 is a flowchart showing a flow when imaging the subject O into which the stents 15, 15A, 15B are inserted by the X-ray diagnostic apparatus 1 shown in FIG.

  First, in step S1, the photographing system 2 is driven under the control of the control system 3. The imaging system 2 corresponds to a plurality of directions from the subject O by exposing X-rays from the plurality of directions to the subject O into which the stents 15, 15 </ b> A, and 15 </ b> B provided with the plurality of markers 17 are inserted. Collect X-ray projection data.

  More specifically, the C-arm 8 is rotated at a predetermined angle by driving a motor 9A and a rotation mechanism 9B provided on the base 9. Then, X-rays are exposed from the X-ray tube 6 toward the subject O set on the bed 10. For this reason, X-rays transmitted through the subject O are detected as X-ray projection data by the X-ray detector 7.

  This X-ray exposure and X-ray projection data detection are repeated while changing the projection angle by the rotation of the C-arm 8. For example, by changing the projection angle at intervals of 1 degree, the intensity distribution of transmitted X-rays for 200 degrees can be collected as 200 patterns of X-ray projection data.

  Depending on the diagnostic purpose, the collection of X-ray projection data can also be performed after the injection of contrast agent. When contrast imaging of the subject O is performed by injecting a contrast agent, the contrast agent is injected into the subject O in advance by a contrast agent injector (Injector) prior to the collection of X-ray projection data. Then, after a certain time has elapsed since the injection of the contrast agent, collection of X-ray projection data is executed at the rotational speed of the imaging system 2 of about 50 degrees / second.

  The X-ray projection data of about 200 frames collected by the X-ray detector 7 in this way is output to the data processing system 4. The X-ray projection data input to the data processing system 4 is converted to a digital signal by the A / D converter 11 and then output to the computer 12.

  Next, in step S <b> 2, the X-ray projection data converted into the digital signal is transferred to the first image reconstruction unit 19. In the first image reconstruction unit 19, 3D volume image data is reconstructed from the X-ray projection data as the first 3D image data by the first 3D image reconstruction processing on the X-ray projection data.

  Various methods are known as image reconstruction processing methods. Here, a case where image reconstruction processing by the filtered back projection method proposed by Feldkamp and the like is performed will be described as an example. Of course, not only the filtered back projection method but also a desired image reconstruction processing method such as a successive approximation method can be used.

  FIG. 6 is a diagram showing the definition of a coordinate system and parameters used in data processing in the data processing system 4 shown in FIG.

  As shown in FIG. 6, a 3D fixed coordinate system (X, Y, Z) and a 3D rotated coordinate system (x, y, z) rotated by an angle φ with respect to the fixed coordinate system can be defined. In this case, the vector r is changed to a vector V having (y, z) as a component on the projection plane Sp by an X-ray cone beam emitted from the X-ray tube 6 which is an X-ray source on the rotating x axis. Projected.

  On the other hand, the image reconstruction area can be defined as a cylinder that is inscribed in the X-ray bundle from the tube of the X-ray tube 6 in all directions. The inside of the cylinder is discretized by a distance d at the center of the reconstruction area of the X-rays projected onto the width of one X-ray detection element provided in the X-ray detector 7. Then, image data at discrete points is obtained. However, the discrete interval is not limited to the distance d, and a discrete interval defined for each apparatus can be used.

但し、式(1)においてW₂は式(2)で表される重み関数である。

When performing image reconstruction processing by the filtered back projection method, 3D image data f generated by the image reconstruction processing is expressed by Equation (1) using the coordinate system and parameters shown in FIG.

In Equation (1), W ₂ is a weighting function represented by Equation (2).

Further, (y, z) in the equation (1) indicates a point at which the vector r is projected by the X-ray cone beam, and is represented by the equation (3).

In Equation (4), * is a convolution operator, P _φ (y, z) is subtraction data obtained from X-ray projection data, W ₁ (y, z) is a weight function, and g (y) is a filter function. It is. The filter function g (y) is a high-frequency emphasis filter for correcting blur caused by back projection calculation. A concrete example of the filter function g (y) is a convolution filter such as a Shepp-Logan filter or a Ramachandran filter.

On the other hand, the weight function W ₁ (y, z) in Equation (4) is expressed as Equation (5).

That is, the image reconstruction process is expressed by Expression (1) to Expression (5). Specifically, first, X-ray projection data for about 200 frames is subjected to subtraction processing with image data for correcting density unevenness. Next, as shown in Equation (4), subtraction data P _φ (y, z) for about 200 frames generated by subtraction is weighted with a weighting function W ₁ (y, z), and then convolved. Filter g (y) is applied.

  Furthermore, 3D volume image data f after image reconstruction can be obtained by performing a back projection operation as shown in Expression (1) on the data generated by the convolution operation.

  Next, in step S <b> 3, the first 3D volume image data is sent to the 3D marker identification unit 20. In the 3D marker identification unit 20, the 3D position in the 3D coordinate system of each marker 17 provided on the stents 15, 15A, 15B is identified based on the first 3D volume image data.

  For this purpose, first, a region having a CT value higher than that of a reference material such as bone is extracted by threshold processing on 3D volume image data. For example, an area where the threshold value is 3000 and the pixel value is 3000 or more is extracted.

  The region extracted with a threshold value of 3000 is metal. Therefore, in addition to the markers 17 provided on the stents 15, 15 </ b> A, and 15 </ b> B, dental treatment metals and the like may be extracted as candidates for the markers 17.

  Therefore, the 3D marker identification unit 20 executes an error process for excluding a marker 17 candidate that is erroneously recognized from the extracted marker 17 candidates. The error processing can be performed by threshold processing that refers to the geometric information of the marker 17 that is known information.

  For example, the stents 15, 15A, 15B are usually present near the center of the field of view. Therefore, a candidate for the marker 17 that is within a certain distance from the center of the photographing field of view can be selected as the position of the marker 17. Thereby, the metal for dental treatment can be excluded.

Alternatively, it is possible to execute error processing using the candidate volume of the marker 17. That is, the volume of the marker 17 is 0.1 mm ³ or less, whereas the volume of the dental treatment metal is 100 mm ³ at the smallest. Therefore, the metal for dental treatment can be excluded by selecting the candidate of the marker 17 whose volume of the region is equal to or less than the threshold as the position of the marker 17.

  As yet another example, error processing using the number of markers 17 is also possible. For example, when ten markers 17 are extracted when the number of markers 17 is eight, two candidates for markers 17 are candidates for markers 17 to be excluded. Therefore, the relative distance between the candidates for each marker 17 can be calculated, and the candidates for the two markers 17 can be excluded in descending order of the relative distance.

  Next, the 3D marker identification unit 20 calculates the centers of gravity of the eight identified markers 17.

  Next, in step S <b> 4, the 3D barycentric position of each identified marker 17 is sent to the marker projection unit 21. The marker projection unit 21 calculates the 2D projection position when the 3D spatial position of the marker 17 is projected onto the projection plane of each X-ray projection data. The 2D projection position can be calculated geometrically based on a projection system corresponding to each projection direction from which X-ray projection data has been collected.

  Next, the marker projection unit 21 calculates the distance between the 2D projection positions of the plurality of markers 17. Then, the 2D projection position of the marker 17 whose distance between the 2D projection positions is equal to or less than the threshold value is excluded. Thereby, the 2D projection position of the marker 17 that may overlap on the projection plane can be excluded from the data processing.

  Next, in step S <b> 5, the calculated 2D projection position of the marker 17 is sent to the 2D marker identification unit 22. The 2D marker identification unit 22 acquires X-ray projection data. Then, the 2D marker identification unit 22 identifies the 2D position on each projection plane of the marker 17 based on X-ray projection data corresponding to a plurality of directions.

  Specifically, the 2D marker identification unit 22 first searches for a minimum pixel value in a certain range around the 2D projection position of the marker 17 on the X-ray projection data. It should be noted that the range to be searched for the minimum pixel value is determined in advance as a range in which the 2D position of the marker 17 may be detected empirically or by simulation or the like according to the degree of instability of the imaging system 2. Can do.

  As an example, an initial range within 300 μm centered on the 2D projection position of the marker 17 is set, and a more detailed range in which a minimum value may exist within the initial range is determined by a known rough search method. You may make it specify as a search range. Conversely, the search range for the minimum pixel position may be within 300 μm centered on the 2D projection position of the marker 17 without setting the initial range.

  When the search range for the minimum pixel position is set in the 2D marker identification unit 22, the search process for the minimum pixel position is executed for the set search range. The smallest pixel value appears as a very narrow negative peak. Therefore, signal processing for detecting a peak with high accuracy is performed.

  A signal from the imaging region, that is, a background signal of the marker 17 and a signal from the marker 17 are superimposed on the X-ray projection data to be searched for the minimum pixel position. Therefore, low-frequency data is first created by applying a low-pass filter to the X-ray projection data in the search range of the minimum pixel position to remove high-frequency components, and subtraction data between the low-frequency data and the X-ray projection data before filtering is acquired. It is desirable to do. Thereby, the data which canceled the background signal of the marker 17 can be obtained.

  Next, the search for the peak position is executed for the search range around the 2D projection position on the subtraction data. Then, by calculating the barycentric position of the X-ray projection data or the subtraction data around the pixel corresponding to the detected peak, the actual 2D position of the marker 17 can be identified with high accuracy.

  Note that the above-described peak detection process is merely an example, and the actual 2D position of the marker 17 on the X-ray projection data may be identified by other methods.

Next, the 2D marker identification unit 22 calculates the shift amount between the 2D projection position of the marker 17 calculated by the marker projection unit 21 and the actual 2D position of the marker 17 identified based on the X-ray projection data. Obtained as correction data. In the correction data (Δy, Δz), the 2D projection position of the i-th marker 17 is (Py _i , Pz _i ), and the identified actual 2D position of the i-th marker 17 is (Qy _i , Qz _i ). Then, it can obtain | require by Formula (6).

  However, in Expression (6), N is the number of markers 17 that are not excluded by the error processing that excludes the markers 17 that overlap on the projection plane. Therefore, for example, when the eight markers 17 are provided on the stents 15 and 15B and the two markers 17 are excluded from the 2D position identification processing in the 2D marker identification unit 22 by the error processing in the marker projection unit 21, N = 6.

  Next, in step S <b> 6, the correction data (Δy, Δz) obtained as the shift amount of the position of the marker 17 is transferred to the second image reconstruction unit 23. The second image reconstruction unit 23 performs a second 3D image reconstruction process on the X-ray projection data by an image reconstruction processing method equivalent to the image reconstruction processing method executed by the first image reconstruction unit 19. Executed.

However, the shift of the position (y, z) at the projection point of the vector r is corrected using the correction data (Δy, Δz). Then, the 3D image reconstruction process is executed using the position (y ′, z ′) of the projection point after the position correction. When the image reconstruction processing method is the filtered back projection method, the position (y ′, z ′) of the projection point after position correction obtained by Equation (7) is used instead of Equation (3). A second 3D image reconstruction process is executed.

  Then, second 3D image data is generated from the X-ray projection data by the second 3D image reconstruction process. The second 3D image data generated in this way is positioned with high accuracy based on the shift amount between the 2D projection position of the marker 17 and the actual 2D position of the marker 17 obtained based on the 3D volume image data. It becomes the corrected data. Therefore, even the struts 16 of the fine stents 15, 15A, 15B can be depicted.

  Next, in step S <b> 7, various processes including a 2D process for displaying the second 3D image data on the display device 14 are executed, and then a display 2D image is displayed on the display device 14. That is, the 3D image processing unit 24 executes 3D image processing for generating 2D image data for display from the second 3D image data. Further, the affine transformation unit 25 executes affine transformation processing such as rotation, movement, enlargement, and reduction of the 2D diagnostic image displayed on the display device 14. Further, the LUT 26 performs gradation conversion of the 2D diagnostic image.

  Therefore, the user of the X-ray diagnostic apparatus 1 can observe an X-ray diagnostic image at an imaging site such as the head of the subject O in which the struts 16 of the stents 15, 15 </ b> A, and 15 </ b> B are clearly depicted.

  That is, the X-ray diagnostic apparatus 1 as described above can reconstruct an X-ray diagnostic image in which a minute position shift is corrected using the position of the marker 17 provided on the strut 16 of the stent 15, 15A, 15B as an index. It is a thing. That is, the spatial position of the marker 17 is identified on the volume image data generated by the first image reconstruction process, and the projected position of the identified spatial position on the projection plane and the X-ray projection data searched for in the vicinity of the projected position are displayed. The second image reconstruction process can be executed with the amount of positional deviation between the actual marker 17 and the position correction data.

  On the other hand, the stents 15A and 15B shown in FIGS. 3 and 4 are provided with a plurality of markers 17 so that all the markers 17 do not overlap on an arbitrary projection plane.

  Therefore, according to the X-ray diagnostic apparatus 1, even if the rotational reproducibility of the imaging system 2 cannot always be 50 μm or less, or even if the patient moves minutely, the struts of the stents 15, 15A, 15B. 16 can be depicted more clearly than before. For this reason, the user can grasp the relationship between the strut 16 and the blood vessel.

  Further, by using the stents 15A and 15B as shown in FIGS. 3 and 4, it is possible to reliably correct a minute position shift using the position of the marker 17 as an index regardless of the projection angle.

(Second Embodiment)
FIG. 7 is a configuration diagram of an X-ray diagnostic apparatus according to the second embodiment of the present invention.

  In the X-ray diagnostic apparatus 1A shown in FIG. 7, the point where the position sensor 31 of the transmitter 30 attached to the markers 17 of the stents 15, 15A, 15B is provided and the detailed functions of the 3D marker identification unit 20 are shown in FIG. Different from the X-ray diagnostic apparatus 1. Since other configurations and operations are not substantially different from those of the X-ray diagnostic apparatus 1 shown in FIG. 1, the same components are denoted by the same reference numerals and description thereof is omitted.

  That is, the subject O into which the stents 15, 15A, and 15B provided with the plurality of markers 17 are inserted is set on the bed 10 of the X-ray diagnostic apparatus 1A. However, a transmitter 30 is attached to each marker 17 of the stents 15, 15A, 15B.

  On the other hand, the imaging system 2 is provided with a position sensor 31. The position sensor 31 receives a radio signal transmitted from the transmitter 30 provided in each of the plurality of markers 17 of the stents 15, 15A, 15B, and the transmitter 30 or the marker 17 based on the received radio signal. It has a function to detect the spatial position. As the algorithm for detecting the position, a known algorithm can be used.

  Therefore, the position sensor 31 is installed at a desired position where the signals transmitted from the transmitters 30 of the stents 15, 15A, 15B can be received with sufficient accuracy. The output side of the position sensor 31 is connected to the computer 12 of the data processing system 4. The detection result of the spatial position of the transmitter 30 or the marker 17 in the position sensor 31 is configured to be output to the computer 12 as digital data.

  On the other hand, the 3D marker identification unit 20 of the computer 12 acquires the spatial position detection result of the transmitter 30 or the marker 17 output from the position sensor 31 and the spatial position detection of the acquired transmitter 30 or the marker 17. Based on the result, it has a function of obtaining the spatial position of the marker 17 in the 3D coordinate system.

  The marker projection unit 21 is configured to obtain a 2D projection position when the 3D spatial position of the marker 17 obtained by the 3D marker identification unit 20 is projected onto the projection plane of each X-ray projection data.

  In the X-ray diagnostic apparatus 1A having such a configuration, the spatial position of the transmitter 30 or the marker 17 is detected by the position sensor 31 based on signals transmitted from the transmitters 30 of the stents 15, 15A, and 15B. Then, the 3D marker identification unit 20 identifies the 3D spatial position of the marker 17 based on the spatial position of the transmitter 30 or the marker 17 detected by the position sensor 31.

  That is, instead of identifying the spatial position of the marker 17 from the 3D volume image data generated by the first image reconstruction processing as in the X-ray diagnostic apparatus 1 shown in FIG. The transmitter 30 is attached and the 3D spatial position of the marker 17 is identified based on the spatial position of the transmitter 30 or the marker 17 detected by the position sensor 31.

  For this reason, according to the X-ray diagnostic apparatus 1A shown in FIG. 7, without performing complicated data processing such as image reconstruction processing twice such as the X-ray diagnostic apparatus 1 shown in FIG. X-ray diagnostic image data whose position is corrected with high accuracy using the position as an index can be generated. As a result, it is possible to obtain an X-ray diagnostic image in which the struts 16 of the stents 15, 15 </ b> A, and 15 </ b> B are clearly depicted as compared with the conventional X-ray diagnostic apparatus 1 shown in FIG. 1.

(Other embodiments)
Although specific embodiments have been described above, the described embodiments are merely examples, and do not limit the scope of the invention. The novel methods and apparatus described herein can be implemented in a variety of other ways. Various omissions, substitutions, and changes can be made in the method and apparatus described herein without departing from the spirit of the invention. The appended claims and their equivalents include such various forms and modifications as are encompassed by the scope and spirit of the invention.

  For example, in the above-described embodiment, an example in which imaging of the subject O into which the stents 15, 15A, and 15B are inserted is performed by the X-ray diagnostic apparatuses 1 and 1A, but also in imaging using the X-ray CT apparatus. If an X-ray detector having a sufficient spatial resolution is mounted on the X-ray CT apparatus, the stents 15, 15A, and 15B can be drawn by the same image reconstruction process. In other words, a highly accurate position correction process using the marker 17 as an index can be executed by an algorithm according to the image reconstruction method. Then, X-ray CT image data having a spatial resolution necessary for rendering the stents 15, 15A, and 15B can be generated by two image reconstruction processes.

DESCRIPTION OF SYMBOLS 1, 1A X-ray diagnostic apparatus 2 Imaging system 3 Control system 4 Data processing system 5 Console 6 X-ray tube 7 X-ray detector 8 C type arm 9 Base 9A Motor 9B Rotation mechanism 10 Bed 11 A / D converter 12 Computer 13 D / A converter 14 Display device 15, 15A, 15B Stent 16 Strut 17 Marker 18 Filtering unit 19 First image reconstruction unit 20 3D marker identification unit 21 Marker projection unit 22 2D marker identification unit 23 Second image reconstruction Unit 24 3D image processing unit 25 affine transformation unit 26 LUT
30 Transmitter 31 Position Sensor O Subject

Claims (6)

Data collection means for collecting X-ray projection data corresponding to the plurality of directions from the subject by exposing X-rays from the plurality of directions to the subject into which a stent provided with a plurality of markers is inserted;
A spatial position of at least one of the plurality of markers is obtained based on the first three-dimensional image data generated by the first image reconstruction processing on the X-ray projection data, and corresponds to the plurality of directions. For each of the X-ray projection data, the projection position of the marker on the projection plane of the X-ray projection data and the two-dimensional position on the projection plane of the corresponding marker obtained based on the X-ray projection data A data processing means for obtaining a second three-dimensional image data by a second image reconstruction process for the X-ray projection data accompanied by a correction using the shift amount ;
An X-ray diagnostic apparatus comprising:   The data processing means corresponds to a marker having a distance between the projection position or the two-dimensional position of a marker that is close to the projection position or the two-dimensional position on the projection plane among the plurality of markers being larger than a threshold value. The X-ray diagnostic apparatus according to claim 1, wherein the second image reconstruction process with the correction is executed using only a shift amount between a projection position and a two-dimensional position.   The data processing means is configured to execute an error process for removing a marker candidate erroneously recognized based on the first three-dimensional image data based on geometric information of the plurality of markers. Item 3. The X-ray diagnostic apparatus according to Item 1 or 2.   The data processing means includes, as geometric information of the plurality of markers, the size and shape of each marker, the distance from other markers, the distance from the center of the strut of the stent, and the first three-dimensional image data. The X-ray diagnostic apparatus according to claim 3, wherein at least one of distances from the center is used.   5. The X-ray diagnostic apparatus according to claim 1, wherein the data processing unit is configured to obtain a spatial position of the marker by a threshold process for the first three-dimensional image data. A position sensor for detecting the position of the transmitter or the plurality of markers by receiving radio signals transmitted from transmitters provided in the plurality of markers;
The said data processing means is comprised so that the spatial position of the said marker may be calculated | required based on the position of the said transmitter detected by the said position sensor or the said several marker. X-ray diagnostic equipment.

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